A vehicle driving assisting apparatus disclosed in JP-A No. 1-161600 and JP-A No. 2002-372585 uses an ultrasonic wave sensor for detecting an obstruction existing in the surroundings of a vehicle. The ultrasonic wave sensor detects such an obstruction by radiating an ultrasonic wave to the surroundings and receiving the ultrasonic wave, which has hit the obstruction and been reflected by the obstruction. When the ultrasonic wave sensor detects an obstruction existing in the surroundings of the vehicle, the driving assisting apparatus reports the existence of the obstruction to the driver.
The driving assisting apparatus of this type is capable of measuring the distance between a vehicle and an obstruction by means of the ultrasonic wave sensor and changing the way of reporting the existence of the obstruction to the driver in accordance with the measured distance. For example, the driving assisting apparatus changes the volume of a sound signaling the existence of the obstruction in accordance with the distance.
In dependence on factors such as the installation location and installation angle of the ultrasonic wave sensor on the vehicle as well as the directional pattern of the ultrasonic wave sensor, however, the sensor may inadvertently detect a body, which has such a small height from the surface of the road that the body does not become as an obstacle to the travel motion of the vehicle, as an obstruction. As a result, the driving assisting apparatus unnecessarily reports the existence of such a body to the driver.
In addition to the ultrasonic wave sensor, other sensors are also known as a sensor for detecting an obstruction existing in the surroundings by radiation of an electromagnetic wave or the like to the surroundings and receiving the electromagnetic wave, which has hit the obstruction and been reflected by the obstruction. The electromagnetic wave is a beam such as an infrared ray or an electric wave. By using such other sensors for detection of an obstruction, however, the same problem also arises as well.
This is because, with a sensor capable of measuring a distance between a vehicle and an obstruction by transmission and reception of a wave, it is difficult to prescribe a measurable range of a target for the sensor installed on the vehicle in terms of the target height from the surface of the road. In addition, the measurable range changes in dependence on factors such as the installation location and installation angle of the sensor on the vehicle as well as the directional pattern of the sensor.
Thus, a driving assisting apparatus provided for a vehicle as an apparatus for detecting an obstruction by use of such a sensor is not capable of detecting only a body having a height becoming an obstacle to the travel motion of the vehicle selectively among bodies existing in the surroundings of the vehicle as an obstruction to be reported to the driver.